Double Push Acoustic Radiation Force (DP ARF) Ultrasound for Monitoring Degeneration in Duchenne Muscular Dystrophy

Double Push Acoustic Radiation Force (DP ARF) imaging will be performed in 3 cohorts of up to 10 boys with DMD and in age-matched boys with no known neuromuscular disorders.

The first DMD cohort will enroll at age 5-6, the second at age 7-8, and the third at age 9-10. The rectus femoris (RF), cranial sartorius (CS), gastrocnemius (GAST), and lateral deltoid (DT) muscles will be targeted for their known phenotypic variation in response to dystrophin deficiency. The RF undergoes early necrosis and fatty deposition, the CS is thought to be relatively spared, and the GAST seems to undergo true hypertrophy. The DT, which undergoes hypertrophy like the GAST, will also be examined to determine if the impact of dystrophin deficiency varies between upper and lower limbs. All boys will be imaged 3 times annually for 4 years. In addition to DP ARF imaging every 4 mos, the boys will undergo standard quantitative muscle testing (QMT) and timed function tests (TFT) of time to standing, 6-minute walk, and 30-feet walk. Age at loss of ambulation will also be recorded for each boy. Boys with DMD generally loose ambulation by age 10, so we expect that the 20 boys in the 7-11 and 9-13 aged cohorts will lose ambulation over the course of this study. The 10 boys in the 5-9 aged cohort will likely not lose ambulation during the study. Because the primary objective of this clinical investigation is to evaluate the potential of DP ARF imaging as a relevant surrogate for monitoring disease progression and response to therapies, the focus of the study will be on correlating DP ARF results to change in functional degeneration and time to loss of ambulation.

There are two experimental components to this study beyond what is standard practice for DMD patients: 1) DP ARF ultrasound imaging of the rectus femoris (RF), cranial sartorius (CS), gastrocnemius (GAST), and lateral deltoid (DT) muscles and 2) standard quantitative muscle testing (QMT) and timed function tests (TFTs) of time to standing, 6-minute walk, and 30-feet walk repeated every four months (three times annually) throughout the four-year duration of the study.

This study will commence with DP ARF ultrasound imaging in the Clinical Neurophysiology Laboratory during the patient volunteer's first regularly scheduled research visit. Patient volunteers are expected to be outpatients. However, if a patient volunteer is an inpatient, DP ARF ultrasound imaging may be performed at the patient volunteer's hospital bedside. Immediately following DP ARF examination, the patient volunteer will undergo QMT and TFTs in the Physical Therapy Department. QMT and TFT will be conducted by trained physical therapists. DP ARF ultrasound imaging, QMT and TFT will be repeated as described above at each of the patient volunteers' twelve regularly scheduled research visits over the four-year study duration. Whenever possible, we will schedule research visits to coincide with other clinical visits to UNC. The patients' parents or caregivers will be compensated $50 per visit to defray the costs of travel to UNC, parking and lunch.

DP ARF will also be performed in 30 boys ages 5-14 with no known neuromuscular disorders. Imaging will be performed as described for the boys with DMD. The DP ARF results obtained in boys with no known neuromuscular disorders will be compared to those obtained in boys with neuromuscular disorders to serve as a control for changes in muscle mechanical property to occur with normal muscle growth and development.

DP ARF ultrasound is a noninvasive diagnostic imaging technology performed using commercially available clinical ultrasound imaging equipment - the Siemens Acuson Antares imaging system equipped for research purposes and VF10-5 or VF7-3 linear array transducers (Siemens Medical Solutions, USA Inc. Ultrasound Division). DP ARF imaging will be carried out by a professional sonographer, faculty and/or graduate student research assistants in the UNC-CH Joint Department of Biomedical Engineering. The sonographer will acquire DP ARF ultrasound data with matched B-Mode (for anatomical reference) in the right RF, CS, GAST, and DT muscles of patient volunteers. Patient volunteers will be asked to lie on an examination table in the Clinical Neurophysiology Clinic (outpatients) or to remain in their hospital beds (inpatients). The head of the exam table/bed may be raised to an approximate 45 degree angle to best visualize the muscles of interest with ultrasound imaging.

Once the patient volunteer is positioned, ultrasound gel will be applied to the patient volunteer's skin surface above the muscles of interest. The ultrasound imaging transducer will then be placed on top of the gel. Once the first muscle of interest is located, DP ARF ultrasound imaging will begin. We will orient the transducer to acquire ultrasound data transverse to the muscle fibers in the middle of the muscle length-wise, with three repeated acquisitions. We will then rotate our transducer 90 degrees to orient the imaging plane parallel to the muscle fibers. The previously imaged cross-section will be positioned in the approximate middle of the imaging field of view, with three repeated acquisitions. Muscle fiber orientation will be approximate, as surmised from anatomy. The DP ARF axial focal depth will be directed to the center of the muscle, approximately 20 - 30 mm.

The length of time for DP ARF data collection in each muscle is estimated to be less than 10 minutes. Once DP ARF imaging is completed on one muscle, DP ARF imaging will be performed on the other muscles of interest. Once all 4 muscles (RF, CS, GAST and DT) are imaged, the study procedure will be completed for the DP ARF imaging portion of the study.

For the second part of the study, beginning shortly (less than 4 hours) after DP ARF imaging is completed, the patient volunteer will undergo clinically standard quantitative muscle testing (QMT) of maximum voluntary isometric contraction (MVIC) in the right RF, CS, GAST and DT. The patient volunteer will also undergo clinically standard timed function tests (TFTs) of (1) time to rise from supine to standing, (2) distance walked in six minutes and (3) time to walk 30 feet.

Patient volunteers' participation will end once both study parts one (DP ARF ultrasound imaging) and two (QMT and TFT) are completed twelve times over 4 years. Therefore, there will be regularly scheduled follow-up visits required of the patient volunteers every four months. The patient volunteer is asked to assent and his parents are asked to permit their son to undergo (1) DP ARF ultrasound imaging of his right RF, CS, GAST and DT muscles, and (2) QMT and TFTs of time to standing, 6-minute walk, and 30-feet walk. No additional procedures or requirements are proposed. Every other aspect of the patient volunteers' care for DMD will be carried out in the normal standard of care as clinically indicated.